Add nacl_helper dependencies to chromevox

Add nacl_helper dependencies to chromevox

This fixes breakage in the unittests due to missing deps on nacl_helper.

BUG=none
TEST=rm out/Debug/nacl_helper; ninja -C out/Debug chromevox_tests;
  ./out/Debug/chromevox_tests

Committed: https://crrev.com/531b62943ec6960ac1014fe9b42a84ce42c379e7
Cr-Commit-Position: refs/heads/master@{#335690}

[spang, 2015-06-22 23:52:32]

The CQ bit was checked by spang@chromium.org to run a CQ dry run

[spang, 2015-06-22 23:52:47]

spang@chromium.org changed reviewers:
+ dmazzoni@chromium.org

[commit-bot: I haz the power, 2015-06-22 23:53:07]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1200133002/1

[commit-bot: I haz the power, 2015-06-23 00:31:16]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-06-23 00:31:17]

Dry run: Try jobs failed on following builders:
  linux_chromium_chromeos_ozone_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[dmazzoni, 2015-06-23 16:55:32]

The CQ bit was checked by dmazzoni@chromium.org

[dmazzoni, 2015-06-23 16:55:32]

lgtm

I've disabled all of the tests temporarily, but this fix is good so let's land
it.

[commit-bot: I haz the power, 2015-06-23 16:56:52]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1200133002/1

[commit-bot: I haz the power, 2015-06-23 17:32:05]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-23 17:32:58]

Patchset 1 (id:??) landed as
https://crrev.com/531b62943ec6960ac1014fe9b42a84ce42c379e7
Cr-Commit-Position: refs/heads/master@{#335690}